The present disclosure relates to a square secondary battery.
Alkaline secondary batteries and nonaqueous electrolyte secondary batteries are used for such purposes as driving power sources for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV), and stationary rechargeable battery systems in reducing output fluctuation in, for example, solar power generation and wind power generation and in peak-shifting grid power to store electricity at night and use the stored electricity in the day time.
As disclosed in, for example, Japanese Unexamined Patent Publication No. 2013-157099, a battery to be used for such purposes is provided not only with a gas exhaust valve to release internal pressure of the battery casing when the pressure increases but also with a current interrupt mechanism to interrupt electrical connection between an external terminal and an electrode body inside the battery casing.
In a technique disclosed in Japanese Unexamined Patent Publication No. 2013-157099, a positive electrode current collector or a negative electrode current collector included in the current interrupt mechanism, a first opening, a second opening, at least one third opening or a cut-out, and projections formed on the second insulating member engage with each other. The first to third openings and the cut-out are formed either on the positive electrode current collector or the negative electrode current collector in the second insulating member.
In Japanese Unexamined Patent Publication No. 2013-157099, a high voltage is still applied to a battery module even after the battery is overcharged such that the current interrupt mechanism is activated to interrupt a current. Hence, if electrolyte adheres to a surface of the insulating member made of resin, the surface could conduct the current. When the current runs through the surface of the insulating member, the surface could carbonize. The carbonized portion could be a cause of reconduction, followed by production of sparks.
In order to reduce such risks as reconduction and sparks, the insulating member can be made of such fluorine resin as perfluoroalkoxy alkanes (PFA) which is hard to be carbonized even though the current runs through the surface of the insulating member. Fluorine resin is relatively soft.
Moreover, in the Japanese Unexamined Patent Publication No. 2013-157099, the second insulating member is latched on, and engages with, a lower first insulating member. This second insulating member can be made of a soft resin material such as the fluorine resin described above. Use of the second insulating member made of the soft resin material can reduce the risk of damage to the second insulating member when the second insulating member and the lower first insulating member are connected to each other. However, the soft second insulating member causes new problems below.
The positive electrode current collector or the negative electrode current collector is connected to a reverse plate. Moreover, the positive electrode current collector is connected to a positive plate and the negative electrode current collector is connected to a negative plate. Then, a fastener is provided to fasten the positive electrode current collector or the positive electrode current collector and the second insulating member together. Thus, the second insulating member receives, through the positive electrode current collector or the negative electrode current collector, the weight of the electrode body including a positive plate and a negative plate.
The second insulating member is connected to the lower first insulating member and supported toward a sealing body. The fastener fastening the positive electrode current collector or the negative electrode current collector and the second insulator together is located closer to the connection between the positive electrode current collector or the negative electrode current collector and the reverse plate than to the connection between the second insulating member and the lower first insulating member. Hence, if the second insulating member is made of a soft material, the second insulating member could be deformed by the weight of the electrode body. The deformed second insulating member changes a state of the connection between the positive electrode current collector or the negative electrode current collector and the reverse plate, causing a possible malfunction of the current interrupt mechanism.
Note that such problems are not limited to the case of using the second insulating member made of a soft resin material. The problems can be caused when the second insulating member is thin or the electrode body weighs significantly.
The present disclosure is conceived in view of the above problems, and intends to offer a square secondary battery including a current interrupt mechanism a working pressure of which is more stable, so that the square secondary battery is reliable.